The present invention relates to a continuous process for the production of anionically-polymerizable polymers in a plug-flow, temperature-controlled reactor.
Various types of polymers can be prepared from different monomeric materials, the particular type formed being generally dependent upon the procedures followed in contacting the materials during polymerization. For example, random copolymers can be prepared by the simultaneous reaction of the copolymerizable monomers. Block copolymers are formed by sequentially polymerizing different monomers.
Useful classes of polymers are synthesized via anionic methods. During anionic polymerization, at least one end of the growing polymer is xe2x80x9cliving,xe2x80x9d i.e., provides a site for additional monomers to add onto the polymer.
An ongoing need exists for a controlled process that allows continuously making controlled architecture polymers via anionic polymerization. Controlled architecture refers to a polymer with a designed topology (linear, branched, star, combination network), composition (block copolymer, random copolymer, homopolymer, graft copolymer, tapered or gradient copolymer), and/or functionality (end, site specific, telechelic, multifunctional, macromonomers). The present invention addresses that need.
Briefly, one aspect of the present invention provides a continuous method of producing anionically-polymerized organic material having controlled architecture, including, for example, homopolymers, random copolymers, block copolymers, and starbranched polymers, and end-functionalized polymers.
One embodiment of the present invention provides a continuous process for making an anionically-polymerized organic material having a targeted architecture comprising
a) introducing into a reactor having one or more temperature controlled sections at least one anionically-polymerizable monomer, at least one initiator, and a solvent such that the monomer concentration is 10 to 50 weight %;
b) allowing the monomer to polymerize as the reaction mixture travels in an essentially plug flow manner through the reactor; and
c) discharging the polymerized organic material.
In other embodiments, the process may further include adding one or more steps between b) and c) above wherein one or more polymerizable monomers are sequentially added to the reaction mixture such that a block copolymer is formed as the reaction mixture continues to travel in an essentially plug flow manner through the stirred tube reactor. Embodiments of the process may also include simultaneously introducing two anionically-polymerizable monomers into the reactor such that a random copolymer is formed. The process may also be used to form star-branched polymers and end-functionalized polymers.
In still other embodiments, the process may further include quenching the polymerized organic material and removing solvent from the polymerized organic material.
This invention is particularly useful when at least one anionically-polymerized monomer is temperature sensitive.
The present invention allows the architecture of the produced organic material produced to be controlled by a number of factors including temperature or temperature profile in the reactor, the molar ratio of monomers to initiators, and monomer addition sequence. These factors affect the molecular weight, polydispersity and structure of the final polymerized organic material.
The average molecular weight of the resultant polymeric material is established by controlling the monomer to initiator ratio. This ratio is established by controlling the respective monomer and initiator flow rates. Narrow molecular weight distributions can be obtained by controlling the temperature of the reaction mixture. Avoiding high temperatures minimizes unwanted side reactions that can result in polymer chains having differing molecular weight averages.
Polydispersity can be influenced by the reaction kinetics of the reaction mixture and the minimization of side reactions, especially when temperature sensitive monomers are present. Maintaining optimum temperatures: in each zone of the reactor can positively influence reaction kinetics. Maintaining optimum temperatures can also advantageously affect the solution viscosity and the solubility of the reactants.
The structure of the polymerized organic material is determined by the sequence of monomer addition(s). Homopolymers are formed when only one monomer type is used, random copolymers when more that one monomer type is introduced simultaneously, and segmented block copolymers when more than one monomer type is introduced sequentially.
For the process of the present invention it is preferable that the temperature profile of the reactor be controllable over time and that the reaction mixture be impelled in a relatively plug flow manner through the reactor. This allows the reaction mixture in the reactor at a given location to be subjected to the same reaction conditions as those encountered by previous and subsequent reaction mixture portions as they pass by the same location.
Maintaining temperature control and movement of the reaction mixture in an essentially plug flow manner are complicated by the exothermic nature of the type of reaction being performed, i.e., anionic polymerizations. The use of anionic polymerization methods for the production of block copolymers containing polar monomers (e.g., vinyl pyridine, and alkyl methacrylates) is complicated by side reactions and solution phenomena associated with the aggregation of these materials in solution as micelles. Adequate mixing and temperature control promote the ability to reproduce the same materials, e.g., having a similar average molecular weight and having a narrower polydispersity index (PDI) than obtained without temperature control. Preferably the PDI of the polymers of this invention is less than 3, more preferably less than 2, and most preferably less than 1.5.
One suitable plug-flow, temperature-controlled reactor is a stirred tubular reactor (STR). Any type of reactor, or combination of reactors, in which a reaction mixture can move through in an essentially plug flow manner is also suitable. Combinations of STRs, including combinations with extruders, are also suitable. Regardless of the type of reactor chosen, the temperature or temperature profile of the reactor is preferably controllable to the extent that a plug of the reaction mixture in a particular location within the reaction zone (i.e., the portion of the reaction system where the bulk of polymerization occurs) at time t1 will have essentially the same temperature or temperature profile as another plug of the reaction mixture at that same location at some other time t2. The reaction zone can include more than one temperature-controlled zone of the reactor. STRs may provide for essentially plug flow of the reaction mixture and can be configured such that good temperature control can be attained, and are therefore useful in getting the average molecular weight of the polymer product to remain close to a target value, i.e., have a narrow polydispersity range.
As used herein:
xe2x80x9ccontinuousxe2x80x9d means that reactants enter a reactor at the same time (and, generally, at the same rate) that polymer product is exiting the same reactor;
xe2x80x9cpolydispersityxe2x80x9d means the weight average cell diameter divided by the number average cell diameter; polydispersity is reported on a polydispersity index (PDI);
xe2x80x9cliving anionic polymerizationxe2x80x9d means, in general, a chain polymerization that proceeds via an anionic mechanism without chain termination or chain transfer. (For a more complete discussion of this topic, see Anionic Polymerization Principles and Applications. H. L. Hsieh, R. P. Quirk, Marcel Dekker, NY, N.Y. 1996. Pg 72-127);
xe2x80x9cliving endxe2x80x9d means an anionically-polymerizable reactive site;
xe2x80x9ctemperature-sensitive monomerxe2x80x9d means a monomer susceptible to significant side reactions of the living ends with reactive sites, such as carbonyl groups, on the same, or a different, polymer chain as the reaction temperature rises;
xe2x80x9cstarbranched polymerxe2x80x9d means a polymer consisting of several linear chains linked together at one end of each chain by a single branch or junction point (See Anionic Polymerization Principles and Applications. H. L. Hsieh, R. P. Quirk, Marcel Dekker, NY, N.Y. 1996. Pg 333-368);
xe2x80x9cbranching agentxe2x80x9d means a multifunctional anionically polymerizable monomer or multifunctional quenching or coupling agent, the addition of which results in the formation of starbranched polymer;
xe2x80x9cblockxe2x80x9d means the portion of a polymer chain in which all the neighboring monomer units (except at the transition point) are of the same identity, e.g., AAAAAABBBBBB is a diblock copolymer comprised of A and B monomer units;
xe2x80x9csegmentxe2x80x9d refers to a block of polymer formed by the addition of a specific monomer or a branching agent;
xe2x80x9cfunctional sitexe2x80x9d means a reactive site other than an anionically-polymerizable site;
xe2x80x9cprotected functional groupxe2x80x9d means a functional unit that is reactive after the removal of a xe2x80x9cprotectivexe2x80x9d group that prevents reaction at a particular site;
xe2x80x9cfunctional quenching agentxe2x80x9d or xe2x80x9cAfnxe2x80x9d means a reactive moiety containing a protected functional group capable of quenching or terminating an anionically produced polymer chain; it becomes attached to the end of said chain;
xe2x80x9cquenching agentxe2x80x9d or xe2x80x9cAnxe2x80x9d means a reactive moiety capable of quenching or terminating an anionically produced polymer chain; it becomes attached to the polymerizing end of said chain; this agent may be multifunctional in nature, thus capable of quenching multiple chains, thereby producing a star-like macromolecule;
xe2x80x9cplugxe2x80x9d means a three dimensional slice of the reaction mixture;
xe2x80x9cresidence timexe2x80x9d means the time necessary for a theoretical plug of reaction mixture to pass completely through a reactor;
xe2x80x9creaction zonexe2x80x9d means that portion of a reactor or reactor system where the majority of reaction occurs; and
xe2x80x9ctemperature profilexe2x80x9d means the temperature or temperatures experienced by a reaction mixture plug over time as it moves through a reactor (For example, if the temperature is constant through the reactor, the temperature profile will have a zero slope; if the temperature increases through the reactor, the profile will have a positive slope);
An advantage of at least one embodiment of the present invention is that the temperature of the reaction mixture can be controlled to such an extent that side reactions are minimized, thereby providing a product with a narrow polydispersity. This is especially advantageous when temperature-sensitive monomers are used.
Another advantage of at least one embodiment of the present invention is that the average molecular weight of resulting polymers can be controlled well by controlling the amount of initiator added to the reaction mixture.
Another advantage of at least one embodiment of the present invention is that various polymer architectures can be tailored and synthesized to be suitable for specific applications.
Another advantage of at least one embodiment of the present invention is that the ability to control the temperature enables the reaction materials to be maintained in solution, which facilitates the desired reaction.
Other advantages of at least one embodiment of the present invention is that it allows for controlled reaction kinetics, optimum reaction mixture viscosity and polymer solubility.